In recent years, light-emitting diode bare chips (hereinafter “LED bare chip”) are attracting attention, further high efficiency and long life compared to incandescent lamps and halogen lamps. Furthermore, with their small size, the LED bare chips are expected to realize small light sources.
One example of light source realized using such LED bare chips is disclosed in Japanese laid-open patent application H08-37357. In the disclosed light source, an LED bare chip, which has two electrodes on the rear surface, is mounted to a conductive land of a substrate via a plurality of bumps.
The trend in recent years is to have a larger area for a p-electrode than for an n-electrode, so as to enhance light extraction efficiency from LED bare chips. In addition, a p-electrode tends to be bonded to a conductive land via a plurality of bumps, whereas an n-electrode is bonded to a conductive land via one bump.
FIG. 1 shows an overall view of a conventional light source in which an LED bare chip is mounted to a conductive land via bumps.
In an LED bare chip 9D, its p-electrode is bonded to a conductive land 943a, via four bumps 955a, 955b, 955c, and 955d (see broken lines) and its n-electrode is bonded to a conductive land 943b via one bump 955e (see a broken line).
In such a light source, whether the LED bare chip 9D is mounted to the conductive lands 943a and 943b has been tested in the following way. Shearing force with a predetermined load is exercised onto the LED bare chip 9D after mounting, to see whether the LED bare chip 9D comes off from the conductive lands 943a and 943b. To be more specific, when the LED bare chip 9D does not come off even by a predetermined load of shearing force, it is considered that the LED bare chip 9D is bonded to the conductive land 943a and 943b, via the bumps. 955a, 955b, 955c, 955d, and 955e, and that the LED bare chip 9D is in electrical connection with the conductive lands 943a and 943b. 
However, even for a light source for LED that has passed the test, with years of use, its LED bare chips may stop lighting up, due to conductivity failure between the LED bare chips and the bumps, or between the bumps and the conductive lands.
This is because of the following characteristics of the conventionally performed test. The predetermined load used in the test is determined assuming that all the bumps have been uniformly bonded with an average strength. Therefore, if four out of five bumps are more firmly bonded than an average strength and the remaining one bump is very weakly bonded, it is still possible to obtain the targeted level of bonding in total.
In such a case, the bump in very weak bonding has a possibility of coming off with years of use. If this bump in such weak bonding is one of the four bumps on the p-electrode, it hardly exercises any effect on the conductivity. However, if this bump is on the n-electrode, it is quite likely to cause conductivity failure between the LED bare chip and the conductive lands, leading to non-lighting of the LED bare chip.
Note that, although with a lower possibility, this problem pertaining to the conductivity failure also arises in a case where more than one bump is used with respect to an n-electrode.